Rube.. you have hit on a topic that has been batted back and forth a lot, however I'll give you the 'nutshell' version of the gazillion threads I have read, and my own experience as an owner of a fine 2007 Norinco.
There are noticable difference in the quality of the Norc/Polytech vs. the SA... but mostly in finish. The American made version has Walnut as the basic wood stock while the chinese has something called chu wood. It had less attractive grain, and was typically saturated in oil.. or perhaps was just areally oily wood to begin with. Never the less, even with a lot of sanding down and cleaning up, it doesnt ever come out looking a good, or feeling as good as walnut.
The metal finish on the Springfields is better looking to my eye as well. It's simply a more clean, polished finish.. and it gives the overall impression that more care was paid to the look of the rifle as a whole. And it's true.. it's as if the Chinese couldn't be bothered fussing over the looks too much.
Now.. besides that? I don't know that there is tons of difference. There are upgrade kits. I got a new spring guide (the round ones) and can really tell no difference from the old one when I'm shooting. It made no difference in the accuracy of the rifle either. You will hear tons of talk about the "soft bolts" of the Chinese rifles.. it's a bunch of bull***t. A number of American firms got totally bent about the fact that the chinese were exporting these things into the USA..(they don't anymore..politics) for 1/3 the price of the domestic ones, and smeared the product.. scaring the hell out of everyone with these stories. "well, if you want to take a chance of the thing blowing a hole through your face.. go ahead!".. that type of thing. Headspace issues? yeah, actually there are a lot of flabby tolerances in these rifles.. like they are made for a standard 7.62 cartridge plus a film of mud on top. I bought into all the hype and held my breath the first 100 rounds I fired, thinking the cases were going to rip apart or something.. but you know what? After 2-3000 or so that I've put through it.. I've stopped worrying.
Look around for stories of catastrophic failuresin the Norinco, and you will find NONE. No exploding recievers, no sheared off bolt lugs. Shoot it with confidence.
So to answer your question.. there is nothing wrong with the Norinco, right out of the box, in so much as functionality. It could be prettier sure.. but does that justify 1500$ more money for a Springfield Armoury..(which itself is just a clone.. M1A isn't a real M14) not a fricken chance. Buy the little parts kits if you want, it certainly wont hurt anything, but even the stock parts are good enough.
You will find that they are fun to tweak and fun to shoot. Even MORE fun to hunt with. And after the hunt, WAYYYyyyy more fun to fondle while watching "Tour of Duty" reruns on History Channel or "Band of Brothers" boxed DVD set! 
Tons of people shooting them, not one "kaboom" as a result of rifle malfunction....there was as a result of bad handloading. You can search that in this forum. 
